1) Field of the Invention
The present invention relates to weed control compositions comprising living fungal cells or metabolites of plant pathogens effective for the control of weeds, especially, barnyard grass (Echinochloa) which is a troublesome weed in the cultivation of economic crops, for example, important crops of Gramineae such as rice and wheat, and also to methods for controlling weeds by using metabolites of such fungi.
2) Description of the Related Art
Regarding control methods of weeds, plant diseases and insects, substantial development has taken place approximately in last 100 years owing to developments in chemistry. As a result, chemical control methods have replaced traditional cultivation control methods. In particular, the rapidly progress of synthesized organic pesticides in the middle Nineteen Hundreds, typified by DDT, led to increased field crop yields, improved quality, farming labor saving, etc., so that the world food production was improved rapidly. Serious problems have, however, arisen in last several years from the use of such synthesized organic pesticides, including environmental pollution and reduced control effects resulted from the occurrence of pathogens and insect pests with acquired pesticides resistance. In recent years, the development of synthetic pesticides is therefore apparently oriented toward higher activity of pesticides. Namely, pesticides are developed these days which are harmless to mammals and produce good effects at low application rates while paying sufficient attention to residuality, environmental pollution and the like. On the other hand, there is recently a growing interest in so-called organic agriculture system in which crops are cultivated without pesticides. People are very concerned with the influence of synthetic organic pesticides to the human body and their influence to the natural environment as mentioned above and in recent years, the interests in biopesticides has increased enormously so a great deal of research and development work is under way with respect to biopesticides. The establishment of a total control system relying upon the combination of a biological control method, which makes use of a natural enemy or the like, and a cultivation or cultural control method involving the use of a cultivation system, such as crop rotation, may be mentioned by way of example.
From the foregoing background, there is a keen demand for the establishment of biological control methods. A great hope is placed especially on the development of biopesticides directly using the living cells of a microorganism and microbial origin pesticides using a physiologically active substance produced by a microorganism. In the field of herbicides, extensive investigations are carried out in recent years on mycoherbicides which use a pathogen against weeds. Mycoherbicides which have already been put on the market include "DeVine" (trade mark; product of Abbott Laboratories Ltd.) and "Coilego" (trade mark; product of Ecogen Ltd.). These two mycoherbicides are employed for the control of strangle vine and northern jointvetch, respectively. In addition, a mycoherbicide effective for the control of sicklepod in peanut and soybean fields is said to be commercially available soon from Mycogen Ltd. Neither mycoherbicide nor microbial origin herbicides are yet available against barnyard grass (Echinochloa spp.) which is a troublesome weed in the cultivation of important crops such as rice and wheat.